Tertiary recovery operation

ABSTRACT

Following completion of a secondary recovery operation at breakthrough of the driving flood at the production wells, additional injection wells are located where the oil saturation in the formation is usually higher, usually adjacent production wells with the new injection wells being located between production wells.

nited States Patent [191 ll loyt 1451 Apr. 22, 1975 TERTIARY RECOVERYOPERATION [75] Inventor: Donald L. Hoyt, Houston, Tex.

[73] Assignee: Texaco Inc., New York, NY.

[22] Filed: Dec. 22, 1972 [21] Appl. No.: 317,580

3,332,485 7/1967 Colburn 166/245 3,354,953 11/1967 Morse 3,477,50911/1969 Arendt 166/245 Primary E.\'aminerFrank L. Abbott AssistantExaminer-Jack E. lEbel Attorney, Agent, or FirmThomas H. Whaley; Carl G.Ries' [57] ABSTRACT Following completion of a secondary recoveryoperation at breakthrough of the driving flood at the production wells,additional injection wells are located where the oil saturation in theformation is usually higher, usually adjacent production wells with thenew injection wells being located between production wells.

11 Claims, 5 Drawing Figures PevAz/r/m/v 14 2 22 ,o JfCO/VD/IPY/NJZWO/V14 544 TERTIARY RECOVERY OPERATION FIELD OF THE INVENTION This inventionrelates generally to the production of hydrocarbons from subterraneanhydrocarbon-bearing formations, and more particularly, to a method forincreasing the efficiency of the production of hydrocarbons therefrom.

DESCRIPTION OF THE INVENTION In the production of hydrocarbons frompermeable subterranean hydrocarbon-bearing formations, it is customaryto drill one or more boreholes or wells into the hydrocarbon-bearingformation and produce formation fluids including hydrocarbons, such asoil, through designated production wells, either by the naturalformation pressure or by pumping the wells. Sooner or later, the flow ofhydrocarbon-bearing fluids diminishes and/or ceases, even thoughsubstantial quantities of hydrocarbons are still present in theunderground formations.

Thus, secondary recovery programs are now an es sential part of theoverall planning for exploitation of oil and gas-condensate reservoirsin subterranean hydrocarbon-bearing formations. In general, thisinvolves injecting an extraneous fluid, such as water or gas, into thereservoir zone to drive formation fluids including hydrocarbons towardproduction wells by the process commonly referred to as flooding."Usually, this flooding is accomplished by injecting through wellsdrilled in a pattern, e.g. the alternating line drive and the morecommonly used S-spot pattern, which may be visualized as a special typeof staggered line drive pattern wherein the separation of the lines ofwells is half the spacing between the individual wells.

When the driving fluid, e.g. water, from the injection well reaches theproduction wells of a direct line drive and a staggered line drive, theareal sweep efficiencies are respectively 57 and 78%, and of a -spotpattern, the areal sweep efficiency is about 71%. By continuingproduction considerably past breakthrough, it is possible to producemore of the remaining unswept portion of the formation, althoughcontinued injection will not reduce oil saturation much further.

SUMMARY OF THE INVENTION It is an overall object of the presentinvention to provide an improved recovery procedure involving initiallythree wells in line as part of a well pattern arrangement for exploitinga hydrocarbon-bearing formation, by locating an additional injectionwell between production wells in the selected pattern, as determined bymodel studies or field observation.

A three well group is arranged in line so that the intermediate well iscompleted for injection and the remaining two wells are completed forproduction. Flooding is initiated at the intermediate well by injectionof a driving fluid, such as water, thereinto and proceeds untilbreakthrough of the flood front occurs at the production wells, at whichtime, injection via the intermediate well to maintain flooding may besuspended or terminated. Then, one or more additional injection wellsaligned with each other and located between the production wells aredrilled into the formation and driving fluid is injected via theseadditional wells to drive formation fluids toward the production wells.In this manner, the formation areas where the highest oil saturation hasbeen determined to be, usually adjacent (or between) the productionwells, can be exploited for more complete recovery, this region beingunswept by the secondary recovery operation, generally.

Other objects, advantages and features of this invention will becomeapparent from a consideration of the specification with reference to thefigures of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 discloses the symbols used inthe remaining figures of the drawing;

FIG. 2 illustrates secondary and tertiary phases of a recovery procedureof a direct line drive;

FIG. 3 discloses two units of an inverted S-spot pattern, a special formof a staggered line drive, and showing the secondary and tertiary phasesof a recovery procedure; and

FIGS. 4 and 5 each disclose two units of an inverted S-spot pattern,further illustrating secondary and tertiary phases of recoveryprocedures.

The objects of the invention are achieved by the use of additionalinjection wells located between production wells where the highest oilsaturation is usually located at breakthrough at the conclusion ofsecondary recovery procedures.

The specification and the figures of the drawings schematically discloseand illustrate the practice and the advantages of the invention withdifferent well patterns, examples of which have been observed inpotentiometric model studies which simulate secondary and tertiaryrecovery operations. The model studies indicate a sweep-out obtained inan ideal reservoir, although the recovery from an actual sweep-out of aparticular field may be greater or less, depending on field parameters.

Throughout the figures of the drawings, the same symbols will bemaintained as disclosed in FIG. 1, viz. a solid circle indicates aproduction well, an open circle with a first'quadrant arrow indicates anoriginal injection well, and an open circle with a fourth quadrantarrow, an additional injection well.

Referring to FIG. 2, there is disclosed symbolically a direct line drivein a secondary recovery procedure, wherein the original injection wellsare aligned with the production wells. Upon breakthrough of the drivingfluid at the production wells, these original injection wells may be puton a stand-by basis till completion of additional injection wellslocated between the production wells. Then, as driving fluid is injectedinto the formation via the additional wells, injection via the originalwells either may be resumed or terminated. In this figure, theadditional injection wells are aligned with each other in rows parallelto the original injection and production wells in the direction of theline drive.

In FIG. 3, the invention is illustrated by two units of an inverted5-spot pattern for a secondary and teritary recovery operation with boththe original and additional injection wells being aligned in parallelrows between parallel rows of production wells, the additional wellsbeing located between production wells.

FIG. 4 also shows two units of an inverted S-spot pattern, wherein, uponbreakthrough of the driving fluid at the comer production wellsfollowing the injection of secondary recovery driving fluid via theoriginal injection well in the center of the pattern, the additionalinjection wells are between and aligned with the corner productionwells.

FIG. 5, showing two units of an inverted 5-spot pattern, illustrates thecombination of the disclosures of FIGS. 3 and 4, with the additionalinjection wells aligned with the original wells and other additionalwells aligned with the rows of corner production wells, the additionalwells being located between production wells.

Thus, there has been shown and described the manner by which a tertiaryrecovery operation may be initiated following the conclusion of asecondary recovery operation after breakthrough of driving fluid at theproduction wells. Tertiary recovery processes can be improved bydrilling additional (or using stand-by) wells in regions of high oilsaturation. Potentiometric model studies can be useful to determine theoptimum locations of new wells. Also, the ratio of tertiary injection toproduction wells (l/P ratio) is an important economic factor, as itindicates how many new wells may have to be drilled.

The table below is a summary of results at breakthrough of tertiaryinjection fluid.

Ratio of Injection to Sweep Efficiency "/1 Production Wells As will beapparent to those skilled in the art in the light of the accompanyingdisclosure, other changes and alterations are possible in the practiceof this invention without departing from the spirit or scope thereof.

I claim:

1. In a method of recovering petroleum from a subterranean, petroleumcontaining formation, said formation being penetrated by at least oneinitial injection well and by at least two production wells, saidformation having been exploited by means of an oil recovery method ofthe type in which an extraneous drive fluid is injected into theinjection well to displace petroleum toward the production wells, theimprovement which comprises:

penetrating said formation after breakthrough of the extraneous drivefluid at the production wells with at least one additional injectionwell drilled into a portion of the formation having a higher oilsaturation than that portion immediately adjacent to said initialinjection well, and

injecting into said second injection well, after breakthrough of theextraneous drive fluid injected into the initial injection well at theproduction wells, an extraneous drive fluid to displace additionalformation fluids toward the production wells.

2. A method as recited in claim 1 wherein said initial injection welland said additional injection well are drilled at essentially the sametime and said additional injection well is held in standby during theperiod when extraneous drive fluid is injected into said initialinjection well.

3. A method as recited in claim 1 wherein said initial injection well isshut in after initiating injection of extraneous drive fluid into theadditional injection well.

4. A method as recited in claim 1 wherein injection of extraneous drivefluid into the initial injection well is continued after initiatinginjecting extraneous fluid into said additional injection well.

5. A method as recited in claim 1 wherein the formation is penetrated bya plurality of initial injection wells and by a plurality of productionwells and said secondary recovery method comprises a line drive.

6. A method as recited in claim 1 wherein the formation is penetrated bya plurality of initial injection wells and by a plurality of productionwells and said secondary recovery method comprises a S-spot pattern.

7. A method as recited in claim 1 wherein said formation is penetratedby at least two production wells and said additional injection well islocated between said production wells and closer thereto than saidinitial injection well.

8. A method as recited in claim 1 wherein said formation is penetratedby at least one initial injection well and by four production wellslocated in 5-spot configuration around each initial injection well. andat least one additional injection well is located between adjacentproduction wells and closer thereto than the initial injection wells.

9. A method as recited in claim 1 wherein the extraneous drive fluid iswater.

10. A method as recited in claim 1 wherein the extraneous drive fluid isgas.

11. In a method of recovering petroleum from a subterranean, petroleumcontaining formation, said formation being penetrated by at least oneinitial injection well and by at least two production wells, saidformation having been exploited by means of an oil recovery method ofthe type in which an extraneous drive fluid is injected into theinjection well to displace petroleum toward the production wells, theimprovement which comprises:

penetrating said formation with at least one additional injection welldrilled into a portion of the formation having a higher oil saturationthan that portion immediately adjacent to said initial injection well,said additional injection well being drilled into the formation afterbreakthrough of the extraneous fluid at said production wells, andinjecting into said second injection well, after breakthrough of theextraneous drive fluid injected into the initial injection well at theproduction wells, an extraneous drive fluid to displace additionalformation fluids toward the production wells.

1. In a method of recovering petroleum from a subterranean, petroleumcontaining formation, said formation being penetrated by at least oneinitial injection well and by at least two production wells, saidformation having been exploited by means of an oil recovery method ofthe type in which an extraneous drive fluid is injected into theinjection well to displace petroleum toward the production wells, theimprovement which comprises: penetrating said formation afterbreakthrough of the extraneous drive fluid at the production wells withat least one additional injection well drilled into a portion of theformation having a higher oil saturation than that portion immediatelyadjacent to said initial injection well, and injecting into said secondinjection well, after breakthrough of the extraneous drive fluidinjected into the initial injection well at the production wells, anextraneous drive fluid to displace additional formation fluids towardthe production wells.
 1. IN A METHOD OF RECOVERING PETROLEUM FROM ASUBTERRANEAN, PETROLEUM CONTAINING FORMATION, SAID FORMATION BEINGPENETRATED BY AT LEAST ONE INITIAL INJECTION WELL AND BY AT LEAST TWOPRODUCTION WELLS, SAID FORMATION HAVING BEEN EXPLOITED BY MEANS OF ANOIL RECOVERY METHOD OF THE TYPE IN WHICH AN EXTRANEOUS DRIVE FLUID ISINJECTED INTO THE INJECTION WELL TO DISPLACE PETROLEUM TOWARD THEPRODUCTION WELLS, THE IMPROVEMENT WHICH COMPRISES: PENETRATING SAIDFORMATION AFTER BREAKTHROUGH OF THE EXTRANEOUS DRIVE FLUID AT THEPRODUCTION WELLS WITH AT LEAST ONE ADDITIONAL INJECTION WELL DRILLEDINTO A PORTION OF THE FORMATION HAVING A HIGHER OIL SATURATION THAN THATPORTION IMMEDIATELY ADJACENT TO SAID INITIAL INJECTION WELL, ANDIBJECTING INTO SAID SECOND INJECTION WELL,AFTER BREAKTHROUGH OF THEEXTRANEOUS DRIVE FLUID INJECTED INTO THE INTIAL INJECTION WELL AT THEPRODUCTION WELLS, AN EXTRANEOUS DRIVE FLUID TO DISPLACE ADDITIONALFORMATION FLUIDS TOWARD THE PRODUCTION WELLS.
 2. A method as recited inclaim 1 wherein said initial injection well and said additionalinjection well are drilled at essentially the same time and saidadditional injection well is held in standby during the period whenextraneous drive fluid is injected into said initial injection well. 3.A method as recited in claim 1 wherein said initial injection well isshut in after initiating injection of extraneous drive fluid into theadditional injection well.
 4. A method as recited in claim 1 whereininjection of extraneous drive fluid into the initial injection well iscontinued after initiating injecting extraneous fluid into saidadditional injection well.
 5. A method as recited in claim 1 wherein theformation is penetrated by a plurality of initial injection wells and bya plurality of production wells and said secondary recovery methodcomprises a line drive.
 6. A method as recited in claim 1 wherein theformation is penetrated by a plurality of initial injection wells and bya plurality of production wells and said secondary recovery methodcomprises a 5-spot pattern.
 7. A method as recited in claim 1 whereinsaid formation is penetrated by at least two production wells and saidadditional injection well is located between said production wells andcloser thereto than said initial injection well.
 8. A method as recitedin claim 1 wherein said formation is penetrated by at least one initialinjection well and by four production wells located in 5-spotconfiguration around each initial injection well, and at least oneadditional injection well is located between adjacent production wellsand closer thereto than the initial injection wells.
 9. A method asrecited in claim 1 wherein the extraneous drive fluid is water.
 10. Amethod as recited in claim 1 wherein the extraneous drive fluid is gas.